Race favourites Wild Oats XI and Ragamuffin Loyal led the fleet around the Sydney Heads as the Sydney to Hobart yacht race began in controversial circumstances with the exclusion of 2003 line honours winner Wild Thing.

The Grant Wharington-skippered super-maxi had failed to submit documents that showed modifications to the boat met safety requirements and race rules, officials told a hastily called media conference less than three hours before the gun today.

"The race committee has worked with the owner of the boat Grant Wharington to allow him up to three hours prior to the start of race to provide the documentation required," Cruising Yacht Club of Australia commodore Howard Piggott said.

"However, this has not been forthcoming - the race committee has no option but to not accept the entry of Wild Thing."

Wharington appeared at the CYCA to enter negotiations with organisers less than an hour before the start of the 628-nautical mile blue-water classic, but officials said the exclusion would stand.

"We're absolutely devastated to be told at the 11th hour we won't be racing to Hobart," Wharington told reporters outside the CYCA shortly before the start of the race.

"We're a bit stuck for words as to why it's happened. We've provided documentation - I've got it in my hand - were given approval on Wednesday that we were able to go, then subsequently withdrawn, so we are absolutely devastated.

"It's required under race rules that the design has to be signed off in accordance with ABS (American Bureau of Shipping) and the wording on this report says quite simply that the information provided and assessment undertaken falls under the ABS guide.

A 20-knot southerly is expected to bash the 76-boat fleet down the coast of New South Wales today, before a nor-east wind picks up early on Thursday.

The exclusion of Wild Thing has meant the event is likely to again turn into a drag race between Wild Oats and Ragamuffin.

Ragamuffin pipped the Mark Richards-skippered Wild Oats by less than three minutes last year for line honours following a tactical tacking duel on the Derwent River just before the finish line.

Richards expected the conditions to favour the bigger maxis though was unsure of whether the race record of one day - 18 hours, 40 minutes and 10 seconds, which the yacht set in 2005, would be challenged.

"It'll be pedal to the metal, don't back off and take the shortest route to Hobart," he said at the pre-race weather briefing on Monday.

"The big boats can do 20 to 30 knots in that northerly.

"So if it hangs in for a couple of hours longer than expected, you can be an extra 60 miles down the track. Or it can go the other way."

Wild Oats, who have installed a massive new headsail and modified their keel in an effort to increase speed in lighter winds, have won the race five times and victory this year would move them within one win of equalling the record of seven held by Morna/Kurrewa IV.